I could be many things from thermostat, control board, wiring, connections, motor, batteries or any of another half dozen items.
unfortunately if it does not happen when a tech is there it comes down to the best educated guess based on the HO input and/or visual clues.
if you have this happen again try turning the thermostat from cool to off, if you have not already, or remove it from the base plate on the wall.
This is the Ask Our Pro's forum. In order to post a response here, you must have verified qualifications and have been approved by the AOP Committee. You may ask a question by starting a new thread.
You can find the rules for posting and qualifications here.
Additional infractions may result in loss of posting privileges.